Construction vehicles, such as motor graders, comprise a hydraulic fluid circuit including an engine-driven pump adapted to communicate pressurized fluid to an implement control circuit. During engine start-up, for example, it is desirable to vent the pump pressure back to a reservoir to thereby reduce the torque loading imposed on the engine. An unloading system for this purpose is disclosed in U.S. Application Ser. No. 337,890, filed on Mar. 5, 1973 by J. E. Dezelan et al for "Pump Unloading Circuit", and assigned to the assignee of this application.
The latter system comprises a foot-actuated pedal whereby an operator can open an unloading valve during engine start-up. Occasionally, an operator in the field will employ the system as a "power pedal" whereby the blade of the motor grader, for example, is improperly used in a side-shifting manner to remove obstacles and the like. In essence, the operator unloads the pump and allows it to reach full speed upon revving-up of the engine to generate fluid pressure peaks up to 6,000 p.s.i., upon actuation of the "power pedal", to thus subject the integrated drive train and hydraulic fluid circuit to potential wear and damage.